1. Field of the Invention
The present invention relates to an audio signal processing apparatus for reproducing audio signals recorded on a recording medium, and more specifically to an audio signal processing apparatus for reproducing audible audio signals, in particular in high speed or forward/reverse direction reproduction mode.
2. Description of the Related Art
When video signals are reproduced by a VTR, pictures can be reproduced in various reproduction modes such as ordinary picture, still picture, quick-motion picture, slow-motion picture, reverse direction picture, etc. In the respective picture reproduction modes, information recorded on a magnetic tape can be reproduced by driving the magnetic tape in a direction the same as or opposite to the travel direction of the magnetic tape driven in the recording operation or at a speed the same as or different from the travel speed of the magnetic tape driven in the recording operation.
In the VTR, further, audio signals can be recorded on and reproduced from a magnetic tape, in addition to video signals. Therefore, when audio signals recorded on the magnetic tape together with video signals are reproduced in a direction and at a travel speed different from those of the magnetic tape driven in the recording operation, the audio signals are to be reproduced under such conditions that the audio signal pitch (the fundamental frequency of sound) differs from the original audio signal pitch and/or the information arrangement on a time axis is reversed to the original information arrangement.
As a result, for instance when the recorded information is reproduced from a magnetic tape in a high speed reproduction mode to confirm the contents of the reproduced picture at high speed, the frequency of the audio signals recorded together with the reproduced video signals are converted to a higher pitch (higher sound fundamental frequency) as a matter of course. Therefore, even if the recorded audio signals are reproduced, it is difficult to understand the contents of the information. Further, when the audio signals are reproduced at high speed and in addition in the reverse direction, since the frequency of the audio signals recorded together with the video signals are converted into the higher pitch and in addition the information arrangement is reversed on the time axis, it is still more difficult to understand the contents of the information.
However, when audio signals are being reproduced by driving the magnetic tape (on which video and audio signals are both recorded) at high speed, if the information contents of the audio signals can be understood clearly together with the reproduced video signals, it is possible to use the VTR in much wider fields. For this purpose, there has been proposed such a video and audio reproducing apparatus provided with such signal processing means that the sound pitch can be converted so that the audio signals reproduced at a high speed and/or in a reverse direction can be restored to the original audio signals. In this apparatus, the audio signals compressed on the time axis in the high speed reproduction mode are divided into a plurality of signal blocks for each predetermined amount of audio information; the signal for each block is sampled at a short sampling period; the sampled digital signals are quantized; the quantized digital signals are stored in a memory; and the digital signals stored in the memory are read from the memory for each block at a long-period reading clock timing so that the read digital signals can be extended on the time axis and thereby restored to the original audio signals.